Old rats are not inferior to young ones in their ability to adapt to repeated sequential exposure to copper sulfate pentahydrate

The quality and longevity of life depend on the ability of a biological system to adapt to continuously changing environmental factors. However, why the success of adaptation varies among individuals and whether there are differences in adaptive reserves between young (3 months old) and aged (20 months old) animals remains unclear. To address these questions, we investigated the relationship between the temporal characteristics of exposure (sequential injection of different doses of copper sulfate pentahydrate, CuSO₄*5H₂O) and adaptive success in young and aged Wistar rats. In addition, the potential to enhance adaptive capacity by a biologically active substance based on exometabolites of Pleurotus ostreatus and Saccharomyces cerevisiae (referred to as the mix-factor" was evaluated. Adaptation success was assessed using Kaplan–Meier survival analysis and haematological and biochemical homeostasis parameters in surviving animals, 1.5 months after exposure to an increased dose of CuSO₄*5H₂O (0.50 mg/g liver). We found that rats exposed to repeated sequential doses of CuSO₄*5H₂O at a pre-adaptive concentration of 0.23 mg/g liver (33% of the lethal dose), followed by an increased dose adapted to the toxic effects successfully. The haematological and biochemical parameters of successfully adapted animals did not differ significantly from those of control animals. Furthermore, the temporal pattern, i.e., the number of pre-adaptation exposures to low doses, influenced resistance to the effects of higher compound doses, indicating hormesis. Aged rats exhibited an adaptive capacity comparable to young rats, demonstrating the ability to undergo hormesis and adapt to the increased dose of CuSO₄*5H₂O. The biologically active "mix-factor" (administered to rats after exposure to pre-adaptive doses of CuSO₄*5H₂O) had a minimal effect on the proportion of aged animals successfully adapting to the subsequent increased dose of CuSO₄*5H₂O, compared to the group of young rats.